1. Field of the Invention
This invention relates to a novel process for recovering hydrocarbons from soil and, more particularly, to a water/surfactant process wherein a carefully selected surface active agent is added to the water to provide a clean separation of the hydrocarbons from the soil while limiting emulsification of the hydrocarbons while minimizing contamination of the water with either hydrocarbon residue or clay from the soil.
2. The Prior Art
The term "oil spill" is commonly used to define an accidental discharge of a liquid hydrocarbon in either a water environment or directly on the soil. To be technically correct, the term should be "hydrocarbon spill" since the material spilled ranges from crude oils to refined products such as heating oils, diesel fuel, gasoline, lubricating oil, and the like. Oil spills can range from a small seepage of a few liters of hydrocarbon liquid to millions of liters, for example, when a supertanker suffers a ruptured hull. However, for purposes of convenience and to conform to the popular vernacular, the term "oil spill" will be used throughout. Various techniques have been implemented for handling an oil spill on water. These include the use of skimmers, containment booms, absorbents, dispersants, and microbial digestion systems. Ultimately, however, a significant portion of the spilled oil reaches shore where it contaminates the soil and thus represents a significant environmental problem. The recovery of oil from oil-contaminated soil is difficult because soil includes a broad spectrum of materials ranging from fine clays to sand, gravel, and rocks along with a certain amount of humus in the form of decaying vegetable matter. As such, an oil spill on soil represents a particularly difficult challenge.
Customarily, it is the practice to treat oil spills on beaches, for example, by absorbing excess oil with an absorbent material and then treating the residual oil on the beach soil with detergents and microbes to break down the remaining oil. An alternative practice is to process the contaminated soil through a high-temperature furnace to burn off the oil. Neither of these procedures is satisfactory since the first process creates unwanted byproducts and the second process is expensive and produces a sterile, undesirable soil residue Importantly, the removal of oil using a surfactant historically has resulted in an emulsion of water and oil with a fine clay suspended therein This emulsion is extremely difficult to process.
One form of a naturally occurring "oil spill" is found in tar sand deposits where the hydrocarbon is present in the form of bitumen dispersed throughout a body of sand, albeit in relatively low concentrations. Certain types of bitumen have an extremely high viscosity and are bonded directly to the grains of sand while others include a thin film of connate water interposed between the bitumen and the sand grains. Numerous processing schemes have been proposed for recovering this bitumen from the tar sand deposits and include thermal processes, solvent processes, water processes, and hybrid combinations of these processes. However, the processing of tar sands, while presenting a fairly complex set of processing problems, is relatively simple when compared to the recovery of oil from a soil contaminated by an oil spill. First, the oil in an oil spill can be from any source; and, second, soil is a highly complex composition that has a wide range of constituents unlike the sand in a tar sand deposit. This means that most, if not all, prior art strategies for processing tar sands to recover bitumen are unusable with regard to recovering oil from an oil spill and returning the cleaned soil to its original location In most cases, conventional, tar sand processing schemes will simply create more problems than are solved when used to recover oil from an oil spill. In particular, the retention of residual oil by the soil must be reduced to an acceptable level while, simultaneously, great care must be taken to assure minimal dispersion of clay from the soil into the cleansing solution, whether an organic solvent or water.
The reference of Martin (U.S. Pat. No. 4,380,268) teaches the removal of paraffin deposits from oil wells. The preferred detergent degreaser comprises a ten or eleven carbon linear alcohol reacted with 6 mols of ethylene oxide and then reacted with a ten carbon linear alcohol For maximum performance, sodium silicate anhydrous is added. The detergent degreaser is diluted with water which has been heated to 130.degree. F.
Clearly, of course, such a detergent degreaser is intended to emulsify and remove the paraffin from the oil well. If the paraffin were not emulsified, the paraffin would separate from the water during the 24 to 48 hour shut down of the well and render the pumping effort during repumping phase difficult if not impossible due to the known plugging effect of paraffin in the well.
It is also important to note that the Martin reference does not teach the removal of oil from soil since it is directed only to removal of paraffin from an oil well. Martin is using this detergent degreaser as a new solvent and, therefore, the concentrations must be high in that the hydrocarbon chain in the surfactant is dissolving the paraffin while the ethylene oxide portion binds the paraffin to the water. This is the regular mechanism by which a surfactant works. The silicate increases the pH of the water which is also essential to enable the surfactant to work in its customary way.
In view of the foregoing, what is needed is a processing strategy for recovering hydrocarbons from soils contaminated as a result of an oil spill while at the same time limiting the formation of an emulsion between the hydrocarbons and the water. It would also be an advancement in the art to provide a processing strategy whereby a soil contaminated with oil can be easily and relatively economically cleaned and, if desired, returned to its original site after the oil has been recovered. An even further advancement in the art would be to provide a water/surfactant process for producing a relatively clean soil while significantly minimizing emulsifying the oil into the water resulting in a significant reduction in the contamination of the water. Such a novel process is disclosed and claimed herein.